FIG. 1 is a simplified side view of a transmitarray antenna. Such an antenna typically comprises one or a plurality of primary sources 101 (a single source in the shown example) irradiating a transmit array 103. Array 103 comprises a plurality of elementary cells 105, for example, arranged in a matrix of rows and columns. Each cell 105 typically comprises a first antenna element 105a arranged on the side of a first surface of the array directed towards primary source 101, and a second antenna element 105b arranged on the side of a surface of the array opposite to the first surface. Each cell 105 is capable, in transmit mode, of receiving an electromagnetic radiation on its first antenna element 105a and of retransmitting this radiation from its second antenna element 105b with a known phase shift ϕ, and, in receive mode, of receiving an electromagnetic radiation on its second antenna element 105b and of retransmitting this radiation from its first antenna element 105a with the same phase shift ϕ.
The characteristics of the beam generated by the antenna, and particularly its shape (or profile) and its central direction (or pointing direction), depend on the values of the phase shifts introduced by the different cells.
Transmitarray antennas particularly have the advantages of having a good power efficiency, and of being relatively simple, inexpensive, and low-bulk, particularly due to the fact that the transmit arrays can be formed in planar technology, generally on a printed circuit.
The article entitled “Wideband linearly-polarized transmitarray antenna for 60 GHz backhauling” of C. Jouanlanne et al. (IEEE Transaction on Antennas and Propagation, vol. 65, no. 3, pp. 1440-1445, March 2017) describes an embodiment of a transmitarray antenna. In this example, the transmit array is a planar structure comprising a stack of first, second, and third conductive layers separated two by two by dielectric layers. Each elementary cell comprises a first conductive pattern formed in the first conductive layer and defining the first antenna element of the cell, and a second conductive pattern formed in the third conductive layer and defining the second antenna element of the cell. The second conductive layer forms a ground plane arranged between the first and second antenna elements. The coupling between the first and second antenna elements is achieved by means of an insulated conductive via crossing the ground plane and connecting the first antenna element to the second antenna element. The value of the phase shift introduced by each cell depends on the geometry of the cell and particularly on the shape, on the dimensions, and on the arrangement of the antenna elements and of the coupling via of the cell.
The article entitled “A V-band switched beam linearly-polarized transmitarray antenna for wireless backhaul applications” of L. Dussopt et al. (IEEE Transaction on Antennas and Propagation, vol. 65, no. 12, pp. 6788-6793, December 2017) describes another embodiment of a transmitarray antenna. In this example, the transmit array is also a planar structure comprising a stack of first, second, and third conductive layers separated two by two by dielectric layers. Each elementary cell comprises a first conductive pattern formed in the first conductive layer and defining the first antenna element of the cell, and a second conductive pattern formed in the third conductive layer and defining the second antenna element of the cell. The second conductive layer forms a ground plane arranged between the first and second antenna elements. In this embodiment, the first and second antenna elements are not connected, the coupling between the first and second elements being performed by means of a slot formed in the ground plane opposite the two elements. The value of the phase shift introduced by each cell depends on the geometry of the cell and particularly on the shape, on the dimensions, and on the arrangement of the antenna elements and of the coupling slot of the cell.
Conventionally, to limit the complexity and maximize the bandwidth of a transmit array, the elementary cells of the array may have a limited number N of configurations (shapes, dimensions and layout of the antenna and coupling elements), corresponding to N different phase shift values. In other words, on design of the array, each elementary cell is selected from among one of the N different configurations, respectively corresponding to N different phase shift values, which amounts to quantizing over log2(N) bits the phase shift introduced by the cells. For example, in C. Jouanlanne et al.'s above-mentioned article, the elementary cells may have N=8 different configurations, which corresponds to a quantization over 3 bits of the phase shift introduced by the cells and, in L. Dussopt et al.'s above-mentioned article, the elementary cells may have N=7 different configurations, which corresponds to a quantization over 2.8 bits of the phase shift introduced by the cells.
In C. Jouanlanne et al.'s above-mentioned article, the transmit array is optimized to operate at a central frequency of 61.5 GHz and has a bandwidth at −1 dB in the range from 57 to 66 GHz, that is, a relative bandwidth at −1 dB of 15.4%.
In L. Dussopt et al.'s above-mentioned article, the transmit array is optimized to operate at a central frequency of 64.3 GHz and has a bandwidth at −3 dB in the range from 58.95 to 68.8 GHz, that is, a relative bandwidth at −3 dB of 15.4%.
It would be desirable to at least partly improve certain aspects of known transmitarray antennas.
In particular, it would be desirable to have a transmit array capable of operating at higher frequencies than known transmit arrays, and/or having a wider relative bandwidth than known transmit arrays, while limiting the number of metal layers used and taking into account the manufacturing limits of the selected technologies.